Unit 2: Nutrition                                                                  1   2   3 

1. Nutrition function

Nutrition is the join of processes that allows living beings obtain matter and energy from the environment in order to perform the vital functions and to grow and to replace the damaged or lost parts of their bodies.

Living beings can be classified by the type of nutrition they have into two groups: autotrophs and heterotrophs.

   a)  Autotrophic nutrition:

Living beings which make their own organic matter from the inorganic matter using any external source of energy are called autotrophs.

Depending on the type of energy they use, autotrophs can perform:

  - Photosynthesis. It is a chemical reaction which uses sunlight energy 

     to synthesize organic matter. Plants, algae and some bacteria are

     photosynthetic organisms.

- Chemosynthesis. The energy to synthesize organic matter comes

   from other chemical reactions which take place inside the own cell.

   Only some types of bacteria are able to perform it.

   b) Heterotrophic nutrition:

Living beings which are not able to make organic matter are called heterotrophs. They have to feed on organic matter produced by other living beings. They transform this food to obtain nutrients and energy. Animals, fungi, protozoa and some bacteria are heterotrophs.

According to the source they obtain their food, they can be:

- Herbivores. They feed on plants.

- Carnivores. They feed on other animals.

- Omnivores. They feed on both plants and animals.

- Saprophytes. They feed on decaying matter.

1.1. Why is nutrition necessary for living beings?

1.2. Classify the following organisms into autotrophs or heterotrophs.

       What criteria have you followed?

1.3. Indicate the main difference between:

       a. Photosynthesis - Chemosynthesis

       b. Autotrophs - Heterotrophs